Emerald ash borer (EAB) has been found in Mitchell County for the first time. Since it was first detected in 2010, the invasive, ash tree-killing insect from Asia has been confirmed in all but six of Iowa’s 99 counties. EAB larvae were collected near Spring Park in rural Osage by the Iowa Department of Agriculture and Land Stewardship and federal identification confirmed the samples were positive for EAB. 

EAB is a major threat to native ash tree species, usually killing a tree within two to four years after becoming infested. Larvae feeding on the inner bark eventually kills ash trees because the feeding cuts off the tree’s ability to transport water and nutrients. Indicators of an infestation can include canopy thinning, leafy sprouts shooting from the trunk or main branches, serpentine (S-shaped) galleries under the bark, bark splitting, woodpecker damage and 1/8-inch D-shaped exit holes.

While adult beetles can move locally by flying, long-distance spread of this insect has been attributed to people moving infested materials, including firewood. People are encouraged to buy locally sourced firewood where it will be burned to help limit the spread of EAB.

Landowners and managers can wait and see what happens for ash trees at risk, remove declining trees and replace them with other species, or use preventive insecticide treatments to preserve and protect valuable and healthy trees. The best time to treat for EAB is in the spring, from mid-April to mid-May. Insecticides are most effective when the ash tree is actively growing and uptake is at its peak. Tree service companies can apply insecticide trunk injections through the summer if soil moisture is available.

Iowa State University Extension and Outreach has produced a publication about EAB treatments, which is available for download here.

Iowa continues to evaluate the spread of EAB on a county-by-county basis. Before a county can be declared positive, a life stage of the insect must be collected and confirmed. Anyone who suspects an infested ash tree in a county not currently known to be confirmed with EAB is asked to contact one of the following organizations as soon as possible:

  • Iowa Department of Agriculture and Land Stewardship, State Entomologist Office, 515-725-1470
  • Iowa State University Extension and Outreach, Entomology, 515-294-1101
  • Iowa Department of Natural Resources, 515-725-8200

Additional information on EAB, including a county detection map, can be found here.